In order to direct a construction machine or more generally a working tool on a construction site, there is a need for determining not only a position of the construction machine along horizontal directions, but also to obtain and control a vertical elevation. There are different methods available for surveying a ground profile and to direct working tools or construction machines accordingly. For example, a system to measure the absolute position can be set up on the basis of GPS (GPS=Global Positioning System). A different system measures local or relative positions with respect to a reference point and uses for example so-called total stations or laser transmitters. Also combinations of both systems are known.
Moreover, simple measuring tools are available that use an existing ground profile as a basis on which a new ground profile is developed.
GPS-based positioning systems, e.g. hand-held or mounted systems, are generally known. To achieve an increased position accuracy different approaches are possible. For example, a reference station or RTK evaluation (RTK=Real Time Kinematics) can be used, and depending on effort and resources position accuracy in a centimeter range is possible.
In systems using the total station, a robot guided measuring station follows a prism mounted on a movable part and transmits the evaluated coordinates to a recipient, that evaluates on the basis of this data a local position of the prism within the construction site. The effort is significant and in systems using the total station only one prism can be followed at a given time, which is disadvantageous although the position accuracy reaches already a sub-centimeter range.
Laser-based systems are used in cases where the knowledge about the elevation above a horizontal or reference plane is more important than the exact position within the horizontal plane. This is, for example, the case for construction at a known position or for underground construction of buildings or drainage.
Conventional laser systems are described in U.S. Pat. No. 4,441,809, in which at least two fan-shaped laser beams are transmitted (for example, having a cross section of a V or an X) so that at each revolution two signals are generated at each detector. A radio unit is used to provide a strobe signal. A further laser system is described in US 2003/0137658, which has no radio unit but uses instead a GPS receiver. The disclosure employs also at least two fan-shaped laser beams.
Also combined GPS- and laser-based systems are known. The GPS signal is used as a coarse elevation information. The laser system transmits fan-shaped laser beams (as a Z-shaped laser beam, for example) and is used to improve significantly the vertical accuracy or resolution, i.e. the information about the elevation along a z-axis. This method is known as millimeter-GPS and combines the advantage of high precision measurement with the possibility of using the system simultaneously by various participants. It is, however, technically very costly.